Incineration of waste materials generally produces bottom ash and flue gases, which may contain particulates. These particulates are called flue dust or fly ashes. These fly ashes are mainly composed of calcium oxide, silicon dioxide and various metal oxides. Normally, the flue gases are subjected to a cleaning step prior to venting into the atmosphere. The bottom ash contains all non-combustible material, typically salts and metals. The metals may be present in their neutral (metallic) form and/or as salts, in which the metals are present in the form of ions. Its composition depends strongly on the feed of the incineration process.
In the art the bottom ash from incineration plants is usually disposed of by dumping or using the material for construction purposes after immobilizing the leachable compounds, e.g. by packing the ash in bentonite.
The availability of metals such as copper has been dropping in recent years as a result of rising demand and the exhaustion of natural resources.
Present methods recover valuable metals such as copper from waste materials using extraction methods based on a combination of magnetic and mechanical extraction. These known methods are not very efficient for removing particles having sizes below 4 mm and are considered infeasible for particle sizes below 1 mm. Furthermore, these magnetic/mechanical methods generally produce scrap metal mixtures, which need to be further refined before they can be reused. Moreover, these methods omit the metal salts, which are the main cause of environmental issues, such as ground water pollution, when above mentioned ashes are used for construction purposes.
EP-A-0 274 059 describes a process for the recycling metals from pyrolysed electrical batteries, assembled print circuit boards and electronic components using electrolysis. The metals collected during the electrolysis step described in EP-A-0 274 059 are then separated from each other following the electrolysis step using known metallurgical or electrochemical methods. However this process has the disadvantage that a further processing step is required to separate the metals following electrolysis. Also, the process of EP-A-0 274 059 is limited in its use to electrically conductive input streams. The present invention seeks inter alia to provide a method that is more versatile so that it may be used also for processing streams that are not, or only slightly electrically conductive. This is in particular the case for bottom ash, which is not electrically conductive.